Various abbreviations that appear in the following description and in the Figures are defines as follows:    3GPP third generation partnership project    BSC base station controller    BSS base station system    BSSGP base station system GPRS protocol    CN core network    CS circuit switched    DRX discontinuous reception    DTM dual transfer mode    DTX discontinuous transmission    EDGE enhanced data rates for global evolution    E-UTRAN evolved UMTS terrestrial radio access network    GANC generic access network controller    GERAN GSM EDGE radio access network    GPRS general packet radio service    GSM global system for mobile communications    Gb interface between GERAN and SGSN    Gs interface between MSC and SGSN    HO handover    IMS IP multimedia subsystem    LTE long term evolution    MAC medium access control    MM mobility management    MS mobile station (e.g., a GERAN terminal)    MSC mobile switching center    MME mobility management entity    MS mobile station    Node-B base station    eNB evolved Node-B    PS packet switched    QoS quality of service    RAN radio access network    RAT radio access technology    RLC radio link control    RNC radio network controller    SGSN serving GPRS support node    UE user equipment (e.g., an E-UTRAN terminal)    UMTS universal mobile telecommunications system    UPE user plane entity    VoIP voice over internet protocol    WCDMA wideband code division multiple access
As a general and non-limiting definition, a circuit switched network is one in which a physical path is obtained for and dedicated to a single connection between two end-points in the network for the duration of the connection. In contrast, a packet switched network is one in which relatively small units of data, referred to as packets, are routed through the network based on a destination address contained within each packet. The use of packets enables the same data path to be shared among a plurality of users in the packet switched network.
In 3GPP the specification of the LTE (E-UTRAN) is ongoing. There is a requirement to provide transitions between GERAN and E-UTRAN in order to maintain seamless mobility across different technologies. There are two characteristics of E-UTRAN that should be taken into account for the development of adequate inter-working solutions: support of packet data only exists in E-UTRAN, i.e., only the PS domain (not the CS domain) is available; and higher QoS requirements in E-UTRAN as compared to what is offered in the other 3GPP systems (e.g., WCDMA, GSM/GPRS/EDGE).
The 3GPP E-UTRAN Inter-RAT handover requirements are specified in 3GPP TS25.913, V7.3.0 (2006-03), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for Evolved UTRA (E-UTRA) and Evolved UTRAN (E-UTRAN) (Release 7), incorporated by reference herein. The main requirements applicable to GERAN/E-UTRAN inter-working are: inter-working with GERAN/UTRAN should be supported; the UE/MS performs inter-RAT neighbor cell measurements during DRX idle periods that are provided by the network through suitable DRX/DTX periods or packet scheduling if necessary; and the maximum service interruption time (E-UTRAN to GERAN/UTRAN) is less then 300 ms for real-time (RT) services, and less then 500 ms for non real-time (NRT) services.
These requirements apply both to terminals (user equipment and mobile stations) and GERAN networks that provide support for E-UTRAN handovers.
Thus, supporting HOs between GERAN and E-UTRAN, and vice versa, with minimum service interruption is an important requirement. In particular, the handover of voice services is critical due to the required domain switch from CS to PS.
Handover of a CS voice call to an E-UTRAN VoIP call (a PS domain call), and vice versa, may be a most challenging case, seeing that there is no CS domain in E-UTRAN, and there are no interfaces to the CS domain, at least as presently envisioned in E-UTRAN 3GPP specifications and technical reports.
The problem that is thus presented is how to perform a handover of CS voice call to a VoIP call from GERAN to E-UTRAN, and vice versa, in a seamless manner as perceived by the user, without service interruption and without quality degradation. Furthermore, considering that currently deployed GERAN networks do not support PS handover, this problem becomes even more challenging.
It is noted that procedures utilizing Voice Call Continuity (VCC) from E-UTRAN to 2G/3 G have been discussed as part of single radio VCC solutions, as in 3GPP TR 23.882 V.1.4.2 (2006-10), 3rd Generation Partnership Project; Technical Specification Group Services and System Aspects; 3GPP System Architecture Evolution: Report on Technical Options and Conclusions (Release 7), incorporated by reference herein.
Reference may also be made to the following documents, which may be generally related to the problems discussed above:
“Handover of packet-switched services in GERAN A/Gb mode”; Rexhepi, V., Bohaty, Hamiti, S. Sébire, G.; Nokia, Helsinki, Finland; Global Telecommunications Conference, 2005. GLOBECOM '05. IEEE; Publication Date: 28 Nov.-2 Dec. 2005, Volume: 5;
“Intersystem Handover Simulation, White Paper”, WPIHOSFN2.1, 26 May 2005, F. Neeser, Nexus Telecom AG, Switzerland;
TSG-SA WG 1 (Services) meeting #6, TSG S1#6(99) 894, San Diego, 29 Nov.-3 Dec. 1999, Agenda Item: All-IP ad-hoc, Agenda Item: 7.1, Source: Orange PCS Ltd, Subject: Handover scenarios for “all-IP” network in release 2000;
US 2006/0281459 A1, Dec. 14, 2006, Marinescu et al., “Utilizing a Same Target Cell During Circuit-Switched and Packet-Switched Handover”, Nokia Corporation;
US 2007/0058791 A1, Mar. 15, 2007, Liu et al.; “Method for Handoff from Packet Switching Domain to Circuit Switching Domain and Equipment Thereof”, Huawei Technologies Co., Ltd.; and
WO 2006/103547 A1, Publication Date: Oct. 5, 2006; “Combined Handover of the Circuit-Switched (CS) and Packet-Switched (PS) Resources”, Marinescu et al., Nokia Corporation.
For example, the above-referenced US 2007/0058791 A1 discloses a method for handoff from a PS domain to a CS domain that includes the MS obtaining a handoff number and initiating a CS domain session request by taking the handoff number as a called number; a network side associating the CS domain session request to an original session of the MS and notifying the MS to finish an air interface handoff; the MS notifying the network side to finish a network side handoff.